Order of the Phoenix

The Order of the Phoenix was a secret society founded by Albus Dumbledore to oppose Lord Voldemort and his Death Eaters. The original Order was created in the 70's 20th century. It was constructed after Voldemort returned to England from abroad and started his campaign to take over the Ministry of Magic and persecute

Muggle-borns. The Order worked with the Ministry to oppose the Dark Lord and his followers, and played a crucial role in the First Wizarding War. Victory came in 1981, with Voldemort's first defeat at the hands of Harry Potter. Victory came with the high cost of many of their members.

The Order disbanded, but was reconvened in 1995 after Harry Potter informed Dumbledore of Lord Voldemort's return. The Ministry refused to admit that the Dark Lord had returned, thus the Order alone worked to protect Harry Potter and the prophecy concerning him and Voldemort in the Department of Mysteries. After anintense battle occurred there on 18 June, 1996 between the Order, Dumbledore's Army, and the Death Eaters, the Ministry finally admitted the truth.

The following year would see the Order losing their leader and the Ministry being conquered by Voldemort. The Order remained an underground resistance, trying to protect Muggles and broadcast the truth during the worst days of the Second Wizarding War. They answered the call to arms by Dumbledore's Army on 2 May,1998, fighting Voldemort and his Death Eaters for the final time at Hogwarts School of Witchcraft and Wizardry. The Battle of Hogwarts ended with Voldemort's death at Harry Potter's hands and a decisive victory for the Order and their allies.

History
The Order of the Phoenix was founded by Albus Dumbledore during Lord Voldemort's first rise to power in the 1970s. Dumbledore formed the Order to combat Voldemort's increasing threat and power. Aurors from the Ministry of Magical so joined the Order to participate in more secretive, sudden assaults aimed to crush the Dark Rebellion. Dumbledore created a method of communication among Order members by inventing a way to make Patronuses speak.

Although the Death Eaters had been attacking mostly Muggles and Muggle-bornsto spread terror, they soon turned to attacking "blood traitors" such as Order members as well. Fabian and Gideon Prewett were murdered by a group of six Death Eaters led by Antonin Dolohov.Caradoc Dearborn disappeared, the Bones family was almost completely destroyed, Benjy Fenwick was brutally murdered, and Marlene McKinnon and her family were murdered by Death Eaters, including Travers. Even as the Order suffered great losses, they continued to fight, and four of their members — James Potter, Lily Potter, Frank Longbottom, and Alice Longbottom — defied Voldemort himself three times.[1]

The Prophecy
This defiance made the two couples and their infant sons Harry Potter and Neville Longbottom targets of a prophecy concerning a person with the power to defeat the Dark Lord. Then Death Eater Severus Snape heard part of the prophecy and reported it to Voldemort, who believed it referred to Harry Potter. He decided to hunt down the Potters, choosing the half-blood Harry, like Voldemort himself, as opposed to the pure blood Neville. The Potters, who were in hiding under the Fidelius Charm, caused Snape to change his side, since he had always been in love with Lily Potter.
 * "The one with the power to vanquish the Dark Lord approaches... Born to those who have thrice defied him, born as the seventh month dies... and the Dark Lord will mark him as his equal, but he will have power the Dark Lord knows not... and either must die at the hand of the other for neither can live while the other survives... the one with the power to vanquish the Dark Lord will be born as the seventh month dies...."
 * —Sybill Trelawney's first prophecy[src]

was not enough to save them, however; the Potters' Secret-Keeper Peter Pettigrew betrayed them, and Voldemort came to their home in Godric's Hollow on 31 October, 1981. He summarily murdered James, but offered Lily a chance to live, as requested by Severus Snape. She rejected the offer, begging for her son's life, and Voldemort used the Killing Curse against her and then on Harry. Because Lily had willingly sacrificed herself out of love for her son, Harry was shielded from the spell, and the curse backfired. Because Voldemort had made Horcruxes, he did not die, but he lost his own physical form. He also inadvertently made Harry himself a Horcrux, as a piece of his soul embedded itself into a scar on Harry's forehead. Pettigrew fled the scene and faked his own death by hiding in his Animagus form (a rat) and cutting off his own finger, while murdering many innocent muggles with one spell, thus Sirius Black was blamed for his crimes, and thrown into Azkaban without a trial.